The range of application for low-power laser initiators, particularly laser diode devices, is somewhat limited. For example, several secondary explosives are not currently amenable to low-power laser initiation. However, the range of application could be substantially extended by thin-film boosters that efficiently absorb the laser energy and explode against an output charge of secondary explosive.
Laser initiation of explosives and pyrotechnics has been well-documented, and results from prompt initiation studies using pulsed, high-power lasers have been reported in the literature for several years. The use of low-power lasers as the energy source in initiators designed to replace conventional low-energy hot-wire devices is an emerging technology. Laser diodes are a particularly attractive energy source. They are small, lightweight, easily packaged, and the optical energy can be delivered using a fiber optic cable that is directly coupled to them. The increased safety and reliability of such optical devices can be substantial, relative to the corresponding hot-wire device. In particular, the electrical hazards due to electrostatic discharge, stray current pick up, and lightning are eliminated.
Known in the art is a technique for optically detonating insensitive explosives using a high-energy Q-switched laser. The high explosive can be housed in a cylinder having a transparent window at one end. The window has a thin metallic coating on its inner side placed so as to be in contact with the explosive. The light energy from the laser vaporizes the metal, detonating the explosive. (U.S. Pat. No. 3,812,783, "Optically Detonated Explosive Device," issued to Lien C. Yang el al on May 28, 1974.)
It is also known to use electro-optics to safely control initiation of multiple igniters in a chain of explosive devices. U.S. Pat. No. H001214, "Multiple Point Laser Detonation System For Explosive Charges," issued to Michael Liva et al on Aug. 3, 1993, describes each igniter connected via a fiber patch cord to a bushing; and U.S. Pat. No. 5,191,167, "Multi-Point Fiber Optic Igniter," issued to Richard A. Beyer on Mar. 2, 1993, describes multiple igniters displaced along a linear fiber optic such that light energy transmitted at an epoxied connection of each igniter will energize an explosive at that location along the fiber optic, thus enabling near simultaneous discharge of multiple explosive devices.
Further, it is also known to transmit energy via fiber optics to the first of two chambers which contains an aspherical glass-focusing head to distribute the initiating light pulse. From there the focused light is sent to a second chamber containing a low-energy laser which initiates the explosive. A secondary explosive, potassium hexanitrodiphenylamine (KHND), is initiated by the laser to a low-order detonation, in turn initiating another secondary explosive, pentaerythritol tetranitrate (PETN), yielding the desired high-order detonation. (U.S. Pat. No. 3,724,383, "Laser Stimulated Ordnance Initiation Device," issued to John A. Gallaghan et al on Apr. 3, 1973.)
There is, therefore, a need for a thin-film optical initiator which amplifies the energy from a low-energy laser source to initiate ignition of an output charge, using relatively insensitive explosives or pyrotechnics, which involves conventional semiconductor manufacturing steps and, therefore, provides an assurance of stability during manufacture and in subsequent use.
Accordingly, it is an object of the invention to provide an alternative initiator to conventional direct irradiation of a reactive charge used in a variety of devices, which is intended to directly replace low-energy hot-wire devices conventionally used to initiate explosive devices.
It is yet another object of the invention to provide a thin-film initiator which amplifies the energy from a relatively low-energy laser source and initiates ignition of the output charge of a device to be set off.
It is also an object of the invention to initiate secondary explosives, such as an organic (CHNO) explosive by a low-power laser, particularly a laser diode, to develop a class of insensitive optical initiators using relatively insensitive explosives, where coupling of the low-energy laser energy with the energetic material is very efficient and reproducible.
It is another object of the invention to provide initiators that are significantly safer to manufacture, handle, and use than existing electronic (hot-wire), percussion, or high-energy laser initiators, particularly in cases where primary explosives are used.
It is also an object of the invention to reduce particle creep effects and gap formation between the thin film and the output charge, which may be less critical than between header and powder in a device using direct irradiation of the granular output charge.
Another object of the invention is to greatly simplify the analysis of the laser light interaction with energetic material in that the thin films have simple geometry and more easily determinable and reproducible optical properties, thus facilitating modeling and design, resulting in decreased testing requirements and time to bring a component into production.
It is also another object of the invention to simplify the performance of optical continuity checks, making them safer than electrical checks, by using very low-power pulses or alternate wavelengths that have minimal interaction with the energetic material.
It is also an object of the invention to fabricate thin-film low-power optical initiators using available thin-film deposition techniques and equipment so that they can be easily mass produced, resulting in little variability between items.
Finally, it is an object of the invention to minimize batch-to-batch variations in production lots of initiators via introduction of a much-simplified composition for the thin-film initiator.